The present invention relates to devices for transmitting and/or receiving laser light; more particularly, to laser transmitting-receiving devices for determining off-aim locations of a target during firing simulations.
Prior-art laser firing simulators which simulate "shots" are known in the art. These prior art laser firing simulators use laser light to simulate a fired projectile or missle from a weapon. Reflected laser light from the hit target is received to both differentiate between a hit and a miss and to determine the location of the hit target in relation to the line of sight of the sighting unit. By knowing the location of the target in the field of view of the sighting unit, a quantitative determination of the accuracy of the aim can be made. Two such prior-art devices are disclosed in West German Auslegeschrift No. 1,703,109 and West German Offenlegungschrift No. 2,149.729.
The laser firing simulator disclosed in the Auslegeschrift causes the laser beam simulating the shot to travel through a scanning pattern in relation to the line of sight. The simulator disclosed in the Offenlegungschrift emits the laser light with pulse coding, either successively or simultaneously. This pulse coded laser light is emitted through a plurality of gapless abutting space angle sectors. Each sector contains a receiving element that can respond to the reflected laser light that is received. Analysis of the sector receive signals generated by the reflected laser light permits a determination of in which sectors a reflection occured. In other words, the target region to be covered is divided into a matrix of individual sectors or fields, and the reflected laser light response signals indicate in which of these sectors the laser light reflecting target is located.
Various problems exist in respect to these prior-art devices. First, the emitted laser light bundles must be produced in such a manner that the space angle sectors are completely filled with laser light without gaps between adjacent sectors. Additonally, the laser light in each sector should be homogeneous and with a high energy density. One such prior art attempt to realize these requirements is to use semi-conductor laser diodes as the laser emitting element. These diodes are arranged in a matrix in the focal plane of an optical projection assembly adjusted to infinity. However, for such an arrangement, the actual light-emitting region for each element (and moreover, in all lasers) is considerably smaller than the total cross-sectional area of the element. For example, the p-n transition layer of a Ga-As laser diode, which generates laser light, has an approximate thickness of only 2 micrometers (um), whereas the total thickness of the laser diode amounts to at least 0.1 millimeter (mm), some fifty times larger. Even if such laser diodes were placed together side-by-side without gaps (an impossibility because of the necessary holders and electrical connections) the external dimensions of each diode, and not those of their active emission region, would determine the magnitude of the space angle sectors and the energy density contained therein. Additionally, a very inhomogeneous distribution of the emitted laser light would occur in every space angle sector.
A proposed solution to obtain homogeneity of the spatial distribution of the emitted light is to use light conductors connected to the light outlet faces of the laser diodes. Even for this solution, the energy density depends upon the external dimensions of the laser diode, and the resulting energy density in the space angle sectors is only a fraction of the energy density which is emitted from the active region of the laser diode.
A second problem in the prior-art devices arises from the fact that, for the arrangements known heretofore for emitting laser light into a number of space angle sectors, a similarly large number of individual lasers or laser diodes is required. For example, if it is desired to divide the total space angle to be covered into a 5.times.5 matrix, 25 laser light emitting elements, controllable with different pulse coding, are required. Consequently, relatively high cost expenditure is required.
Therefore, it would be advantageous to provide a laser firing simulator which achieves a homogeneous energy density in each space angle sector to completely cover any target in the field of view, and to reduce the number of laser emitting elements required to accomplish this result.